viewers: default mic to dB(L) + add Mic-unit toggle (dBL ↔ psi)

The sidecar-modal waveform plot was rendering mic in raw psi, while the
rest of SFM (history table column, peaks block, live-device chart,
event detail modal mic field) had already converted to dB(L) — matching
the BW Event Report convention.  Unifying.

Both viewers now:
  - Default mic chart values + axis title + peak label to dB(L)
  - Provide a header toggle ("Mic: dBL" pill) to flip to psi
  - Persist the preference via localStorage (sfm_mic_unit)
  - Re-render the open chart immediately on toggle

Conversion: dBL = 20 * log10(psi / 2.9e-9), where 2.9e-9 psi is the
20 µPa reference pressure already defined for the rest of the webapp.
Non-positive psi samples (log undefined) render as null; Chart.js
handles them as gaps in line mode and missing bars in histogram mode.

Also fixes event_browser.html's stats table — the MicL row was
hard-coding "<value> psi"; now honors the same toggle.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

sfm/event_browser.html

@@ -289,7 +289,12 @@
   </select>
   <input type="search" id="event-filter" placeholder="filter events…" />
   <span class="pill" id="count-pill">—</span>
-  <button id="print-btn" onclick="togglePrintView()" style="margin-left:auto;background:#21262d">Print view</button>
+  <button id="mic-unit-toggle" style="margin-left:auto;background:#21262d"
+          onclick="_setMicUnit(_getMicUnit() === 'dBL' ? 'psi' : 'dBL')"
+          title="Toggle mic display unit (dBL ↔ psi). Persists across page loads.">
+    Mic: dBL
+  </button>
+  <button id="print-btn" onclick="togglePrintView()" style="background:#21262d">Print view</button>
   <button id="reload-btn" onclick="loadSerials()">Reload</button>
 </header>
 
@@ -328,6 +333,29 @@ const CHANNEL_COLORS = {
 };
 const CHANNEL_ORDER = ['MicL', 'Long', 'Vert', 'Tran'];
 
+// Reference pressure for dB(L) — 20 µPa expressed in psi (≈ 2.9e-9 psi).
+const DBL_REF = 2.9e-9;
+
+// User-toggleable mic display unit: 'dBL' (default, matches BW printout
+// + the rest of SFM) or 'psi' (raw sample unit).
+function _getMicUnit() {
+  return localStorage.getItem('sfm_mic_unit') === 'psi' ? 'psi' : 'dBL';
+}
+function _setMicUnit(u) {
+  localStorage.setItem('sfm_mic_unit', u === 'psi' ? 'psi' : 'dBL');
+  _refreshMicUnitToggle();
+  if (currentEventId) loadEvent(currentEventId);
+}
+function _refreshMicUnitToggle() {
+  const b = document.getElementById('mic-unit-toggle');
+  if (b) b.textContent = `Mic: ${_getMicUnit()}`;
+}
+// psi → dB(L).  Null for non-positive (log undefined; Chart.js renders as a gap).
+function _psiToDbl(psi) {
+  if (psi == null || !(psi > 0)) return null;
+  return 20 * Math.log10(psi / DBL_REF);
+}
+
 // Adaptive decimal formatter — scientific notation only for truly extreme
 // values.  Normal-range peaks render as plain decimals with sensible
 // precision (was previously forcing toExponential(3) which produced ugly
@@ -502,6 +530,19 @@ function renderMeta(data, ev) {
     ['Vert', ev?.vert_ppv],
     ['Long', ev?.long_ppv],
   ];
+  // Mic display honors the current user preference (dBL default).
+  // mic_ppv is stored as raw psi on series3 events; convert when needed.
+  const micPsi = ev?.mic_ppv;
+  const micUnitDisplay = _getMicUnit();
+  let micStr;
+  if (micPsi == null) {
+    micStr = '—';
+  } else if (micUnitDisplay === 'dBL') {
+    const d = _psiToDbl(Number(micPsi));
+    micStr = (d != null ? d.toFixed(1) : '—') + ' dBL';
+  } else {
+    micStr = Number(micPsi).toExponential(2) + ' psi';
+  }
   const statsHtml = `
     <table class="stats-table">
       <thead>
@@ -509,7 +550,7 @@ function renderMeta(data, ev) {
       </thead>
       <tbody>
         ${rows.map(([ch, ppv]) => `<tr><td>${ch}</td><td>${fmt(ppv)}</td></tr>`).join('')}
-        <tr><td>MicL</td><td>${fmt(ev?.mic_ppv)} psi</td></tr>
+        <tr><td>MicL</td><td>${micStr}</td></tr>
       </tbody>
     </table>
   `;
@@ -560,11 +601,11 @@ function renderWaveform(data) {
   );
   const lastDataCh = channelsWithData[channelsWithData.length - 1];
 
+  const micUnit = _getMicUnit();
   for (const ch of CHANNEL_ORDER) {
     const chData = channels[ch];
     if (!chData) continue;
-    const values = chData.values || [];
-    if (values.length === 0) {
+    if ((chData.values || []).length === 0) {
       // Render an empty card so user sees the channel exists but is missing
       const wrap = document.createElement('div');
       wrap.className = 'chart-wrap';
@@ -579,9 +620,19 @@ function renderWaveform(data) {
       continue;
     }
 
-    const unit = chData.unit || 'unit';
-    const peak = chData.peak;
+    // Mic channel: convert from raw psi to dB(L) when the user prefers dBL
+    // (the default).  We mutate `values`, `peak`, and `unit` locally so the
+    // chart datasets + axis title + tooltip + peak label all stay aligned.
+    let values = chData.values || [];
+    let unit  = chData.unit || 'unit';
+    let peak  = chData.peak;
     const peakT = chData.peak_t_ms;
+    if (ch === 'MicL' && unit === 'psi' && micUnit === 'dBL') {
+      values = values.map(_psiToDbl);
+      peak   = _psiToDbl(peak);
+      unit   = 'dB(L)';
+    }
+
     const peakLabel = peak != null
       ? `peak ${_fmtPeak(peak, unit)}`
         + (!isHistogram && peakT != null ? ` @ ${peakT.toFixed(1)} ms` : '')
@@ -781,6 +832,9 @@ document.getElementById('serial-select').addEventListener('change', e => {
 });
 document.getElementById('event-filter').addEventListener('input', applyFilter);
 
+// Reflect any persisted mic-unit preference in the header pill on load
+_refreshMicUnitToggle();
+
 // Initial load
 loadSerials();
 </script>